Process for purification of laundry waste



Aug. 29', 1939. o. M. URBAIN Er Az.

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PROCESS FOR PURIFICATION `OF LAUNDRY Filed Feb. 13, 1937 Mto Patented Aug; 29, 1939 unirsi) sraras Pare-Nr- Ormea PROCESS FOR PURVFICATION 01E' LANDRY STE @liver M. 'Urbain and William R. Sternen, @o-

lumbus, Ohio, assignors to Charles lll. Lewi Hamster, @hic application February is, i937, serien No. reacts 6 Claims.

This invention relates to a process for the purification of laundry waste and has for its object the provision of a simple and advantageous process through the medium of which the highly putrescible waste from laundries can be completely p uried and an eiuent obtained in` the form of sparkling clear water that. may be either reused in the laundry or directly discharged into the receiving stream since it presents no further contaminating problem.

To the end that the purposes and objects of the invention may be made more clearly apparent,

brief reference to the nature of the problem Will rst be made.

The water used for laundry purposes is iirst softened usually by either the zeolite method or the lime-soda-ash methold. A water having a zero hardness content is to be desired since the Y, lower the hardness content, thev greater the savingv in soap costs, which represent one of the Y largest items of expense in the operation of power laundries, exclusive of course of the cost of labor.

The materials washed in a laundry are usually run through from four to six progressive changes lof suds, which constitutes the actual washing operation. After this treatment of the materials in the suds, 'they are run through from ve to seven progressive changes of rinse Water. The temperature of the suds water is usually maintained around 160 F.vwhile the temperature of the rinse water is ordinarily around 150 F.

In additionptothe soaps employed in the formation of the suds, so-called soap builders are also employedto aid the soaps in removing the dirt from the materials Washed. :The soap builders are alkaline in reaction and usually consist of sodiumsilicate, trisodium phosphate, sodium. carbonate, or like materials. When thematerials washed require bleaching, a .small quantity of such bleaching agents as sodium hypochloritev or sodium fluoride is added. Small quantities of aniline and starch are also usually employedin both the washing and the rinsing steps.

From the foregoing it is evident that the laundry waste carries a great variety of substances, both organic and inorganic'. In addition to all of the soapsand chemicals that are employed in the washing and rinsing operations,A the waste also .contains the dirt removed .from the material washed as well as a multitude of various types of bacteria. Roughly, about 45% of the Waste waters discharged by laundries originates from the washing or suds solution while the remaining 55% originates in the rinsing operation.

The wash waters or suds usually contain'froml (ci. 21o-2) y 0.25 gram to 5.0 grams of fatty acids per liter.

Fatty acids are, of course, present in the form as well as many types of bacteria including some pathogenic varieties.

The-hydrogen ion concentration of the suds waters expressed in terms of the pH scale varies from around pH 8.1 to pH 13.8, While the pH of the rinse Waters will vary'from around pH 7.0 to pH 8.6.. The ten-day biological oxygen demand of a `typical 'laundry waste will vary from 2,20 parts per million to 900 parts per million. The waste, it.will therefore be appreciated, is of a highly putrescible character and constitutes a serious problem in the successful operation of `a municipal sewage treating plant operating on biological principles. In fact laundry Waste pre-v sents such a serious problem that in many cities no attempt is made to treat the same in the sewage disposal plant.

Soaps exist in the laundry waste in the formof -semi-colloids. These soaps hydrolyze rather freely even in strong solutions. When one makes an ultrafltration of a soap solution, the fatty acid formed as a result of the hydrolysis of the soap will pass freely through the colloidal membrane While the unhydrolyzed soap portion is retained on the membrane. 'This establishes the fact that the soaps do hydrolyze freely and that theydo exist in solution as semi-colloids. Additionally the soaps in the laundry waste act as protective colloids, stabilizing ne suspensions which otherwise would not exhibit colloidal properties; In other words, the soaps peptize `other substances and thus materially complicate the colloidal structure of the waste. y

It is, therefore, evident that when the soaps are removed from .laundry waste, the colloidal structure ofthe Waste is more or less completely shattered since the soaps constitute a stabilizing factor controlling the entire colloidal structure of the Waste. n l

The present' process'is concerned with eifecting hydrolysis of the soaps to free their fatty acid content and to then removethe fatty acidsfrom the waste, thus destroying the stabilizing factor due to the presence of the soap, and inally removing the waste.

Coming now to a ldescription of our process,

remaining organic matter fromA the reference will be made, for purposes of clarifica- .Y

trating the manner of carrying out the process;

and

Figure 2 isa detail diagrammatic illustration of an appropriate construction for use in the principal filtering steps of the process.

Inasmuch as it is necessary to effect hydrolysis of the soaps in the laundry waste in order to free the fatty acid content thereof, we will first briefly refer to this procedure. When a dilute acid, such for example as dilute hydrochloric acid, is added to laundry waste, the fatty acids are released from the soaps in accordance with the general reaction which follows: I

R.COO.Na+HCl- R.COOH+NaCl Soap Fatty acid A specific example of the general reaction above is given as follows:

C1'1H35.COO.Na-i-HCl-)CizHaaCOOH-i-Nacl Sodium stearato. Stearic acid The above reactions take place at all pHs below ph 7.0, but even at pHs above pH 7.0 the It should be noted that this reaction is of the reversible type. If the fatty acid formed on the right is removed, the hydrolysis of the soap Will proceed to completion. In other words, as long as the pressure is eliminated from the right side of the reaction, it`will continue to move to the right.

A specific example of the .hydrolysis of a soap is given in the following reaction: Y

Sodium palmitate Palmitic acid In accordance with our process, we effect removal of the fatty acids as fast as released from the soaps by hydrolysis so that the hydrolysis reaction continues to completion.

Referring now to Figure 1, the laundry waste is iirstsupplied through the line I to a suitable screening unit 2 of conventional design to remove solids therefrom. From the screening'unit 2, the waste is passed through the line 3, 3 to one of the alternate parallel sand filters 4, 4', also of conventional form, wherein additional solids are removed from the waste to prevent fouling of the subsequent filters. The sand filters 4, 4 are adapted to be alternately employed, and a water.

line 5 with suitable connections 6 and 1 is provided for-backwashing the sand filter not in use. From the sand filter 4 or 4', the waste freed from the solids removed by the screening unit 2 and the sand filter is thence passed through the line 8 or 8 to the fatty acid removing filter 9 or 9. The cross connection l0 between the lines 8 and 8 and the valves Il provide for selective passage of the Waste from either sand filter 4 or 4 to either of the filters 9 or 9'. v

The nature of the filtering medium employed for removing the fatty acids constitutes an important .feature of the present invention. In the present process, the filtering medium employed in the filters 9 and 9' for effecting removal of the fatty acids released from the soaps as a result of hydrolysis due to the addition of the dilute acid through the line designatedv l2 constitutes a ltering medium of high surface area impregnated with zinc oxide.

Zinc oxide has a solubility of 0.001 gram in' 'Y 100 cc. of water at 20 C. at the saturation point sol obviously very little of this reagent will be lost upon passage of the laundry waste through the lter 8 or 9'. The carrier for the zinc oxide may preferably constitute either hard coke or magnesia silicate brick. Both ofvthese materials have an enormous surface area and are both extremely porous and relatively inert chemically. Additionally they will both withstand high temperatures and yet maintain their physical structures, The filtering medium is preferably employed in the form of a granular mass, the individual granules of which will pass a five-mesh screen and be retained upon a twenty-mesh screen.

To obtain the filtering medium impregnated with zinc oxide, the carrier may be pickled in a saturated solution of zinc nitrate until the granules of the carrier are thoroughly saturated with the reagent. The excess 4reagent is then drawn off, and the granulated mass is dried in a current of warm air at about 120 C. and then ignited at a. temperature ranging from 600 to 900 C. At this temperature the zinc nitrate is converted to zinc oxide. 'Zinc chloride may be used in the preparation of the filtering medium in lieu of zinc nitrate. Obviously, regardless of the source from which the medium is derived, theactive agent in the filter constitutes zinc oxide. l

It will thus be observed that the filtering agent in the filters 9. and 9 is made up of a granular mass impregnated with zinc oxide.

As has been pointed out above, when a dilute acid, such for example as dilute hydrochloric acid, is added to laundry Waste, the fatty acids are released from the soaps. This acid may be added to the laundry Wastes either before or after the wastes are passed through the sand filters. In Figure 1, the dilute acid is added through line I2 afterthe laundry wastes have been screened.

Bearing in mind that, due to the addition of the dilute acid, the soaps in the Waste are undergoing hydrolysis at the time the solution reaches the filter 9 or 9 and there is thus present in the I waste free fatty acid, the following reaction takes place in the filter:

' zno+2R.CooH- =zn oocR 2+H2o Fatty acid Zinc salt of fatty acid From the above reaction, it is seen that there is formed on the surface of the granules in filters 9 and 9' a zinc salt of the fatty acids. When the material has become exhausted, it can be regenerated andthe fatty acids released by passing superheated steam through the material. The reaction is as'follows:

Zn(OOCR) 2+Hv2O=ZnO+2R.COOH

Zinc salt of Steam Fatty acid fatty acid Y It should be noted that the first reaction is dependent upon the speed of the' hydrolysis of the fatty acid salts, but since We are removing the fatty acids as fast as they are released by hydrolysis, the hydrolysis reaction proceeds with great rapidity and the whole procedure requires less than fteen minutes, provided of course that the ZnO is at all times in excess of the fatty acid content. The regeneration of the filter is complete within a period of a. few minutes as hot steam breaks down the zinc salts of the fatty acids very readily and very easily.

In the drawing we have disclosed a steam line I3 having connections I4 and I4 for supplying steam to the filters 9'and 9', respectively, for the purpose of driving out the fatty acids. The

steam carrying the fatty acids passes through the filters 9 vand 9', through the lines `I5 and I5' respectively to a suitable condenser I6, and thence to a receiver Il and finally to an evaporator I8 wherein the water may be separated and the fatty acids recovered.

Returning now to the remaining waste constituting the filtrate leaving the filters 9 and 9', this fatty acid free material is next passed through the line 4B or 48' to the chlorinated coal filter I9 or I9', a cross connection 2U and suitable Valves 2l and. i9.

The chlorinated coal constituting the filtering medium with which the filters i3 and lsf' are charged may be prepared in accordance with the teachings contained in United States Patent No. 2,029,962, issued to us on February 4, 1936. The chlorinated coal filter functions to remove the remaining organic polluting substances from the waste. The steam line i3 is provided with an extension 22 and connections 23, 23 for supplying steam to the lters i9 and i9' for purposes of regenerating these filters. The filtrate from filters I9 and i9 constitutes acompletely puried eiiluent and. is discharged through the lines 26 or 2t either to the sewer or for recirculation as a fresh water supply to the laundry.

The steam that is introduced to the filters l@ and i9 for thepurpose of regenerating the same passes out through the lines 25 or 25' to a suitable condenser 26, and the resultant Water carrying the organic matter and substances removed from the filters I9 and 'I9' is discharged into a suitable sump 2i where Ait may be subjected to further treatment and from where, after a time period of oxidation, it may also be discharged into the sewer since it will no longer have any substan- 2wherein the main filter chamber 28 is a sheet chamber 28 and serves to supply steam for the regeneration of the filtering medium. The steam carrying the fatty acids remaining in the filters 9 or 9' andthe organic substances removed from the chlorinated coal filters I9 and I9' may pass out through the line 39 controlled by a suitable valve 40 to the condenser 4I.I

lIn the case of the filters 9 and 9', thecondenser 4I- may discharge through a line 42 controlled by a suitable valve 43 into an appropriate evaporator 44 forrecovery of the fatty acids` Additionally, during the time the steam issupplied, some condensation may occur in the filtering medium 3| carrying with it recoverable fatty permitting alternate use ofthe lters i9v acids. 'I'his condensate may, by closing the valve 36 and opening valve 45, be supplied through the branch line 46 to thel evaporator along with the condensateA from the condenser 4l.

v It will be understood that the invention of the present application is a process and that the apparatus is merely diagrammatically illustrated for the purpose of .lending clarification to the description of the process and that the invention is not to be limited to the employment of any particular apparatus.

To give some idea of the capabilities of the process, the requirements of a laundry discharging upto fty thousand gallons of waste per day can be met through the employment of lters corresponding to the filters 9, 9', i9, and i9', not substantially larger than four feet in diameter and ten feet in height. In use, these filter chambers are not subjected to any extreme pressure forces or to excessive temperatures and, therefore, can be produced at a minimum cost. The condensers for handling the steam and contained substances issuing from the filter chambers 9, 9', i9, and i9 need notbe excessively large, for a laundry discharging up to fifty thousand gallons of waste per day, since the condens-ates taken ofi from these filters will not exceed around four hundred gallons each.

The fatty acids recovered as an incident to the process render the purification process a profitable procedure rather than an economic burden. f

It is to be understood that the foregoing de'- scription is illustrative only and is not to be considered in a limiting sense, the inventionbeing comprehended by the appended claims.

Having thus described our invention, what we claim is: v

1. A process for purifying laundryI waste com-v prising initially removing suspendedsolids from the waste, effecting hydrolysis of the soap soin-: v tion, passing the solution through a lter charged with zinc oxide to remove through chemical reaction-the fatty acidsv freed by the hydrolysis, and thence passing the fatty acid f-ree solution through a chlorinated coal filter to effect removal of remaining organic matter therefrom.

2.. A process for purifying laundry waste comprising screening and filtering the waste to remove solids, adding a dilute acid capable of effecting hydrolysis of the soap solution, passing the solution through a filter charged with zinc oxide to remove through chemical reaction fatty acids as freed by the hydrolysis reaction, then subjecting the fatty acid free solution to the action of chlorinated coal to remove further or- Aganic compounds, and finally discharging the drolyzing the soap solution in vthe waste, removing the fatty acids by passing the waste through a lter charged with zinc oxide and subsequently passing the residual liquids through a filter charged with chlorinated coal.

4. A process for purifying laundry waste comprisingpassing the waste through instrumentalities capable of physically separating solids therefrom, hydrolyzing the soap solution contained therein removing the fatty acids by passing the waste through a filter composed of inert granular material charged with zinc oxide, and finally passing the solution through a second filter containing chlorinated coal.

5|. A process for obtaining purified liquids from 4 f ainda? laundry waste which comprises-passing said waste through a screen to remove solids therefrom, acidifying to free fatty acids by hydrolysis of the soap solution contained therein, ltering to remove suspended particles, removing fatty acids by reaction with zinc oxide, and removing soluble organic impurities by means of chlorinated coal.

6. A process for removing organic and inorganic impurities from laundry waste comprising the steps of acidifying to hydrolyze the soap solution, ltering to remove solid materials, contacting with zinc oxide to chemically remove fatty acids therefrom, and filtering through chlorinated coal to remove soluble organic impurities.

' OLIVER M. URBAIN.

WILLIAM R. STEMEN. 

